Contra Costa, CA: Property Tax Appeal Instructions (2025-26)

Key facts at a glance

The 60-second primer

Your property tax value is the lower of (a) your Prop 13 factored base-year value, or (b) market value on January 1, the lien date. If the January 1 market value is lower, you can receive a temporary Prop 8 reduction for that year. The Assessor rechecks Prop 8 values annually and can raise them more than 2% as the market recovers, but never above your Prop 13 track.

Every California county handles appeals differently. If you own property in multiple counties, you might want to review procedures for Alameda, San Francisco, or browse all our California county guides.

New to property tax appeals? Start with the fundamentals in our Appeal 101 article, which covers the core concepts that apply across California.

The Contra Costa "Informal" route (Prop 8 review)

Most homeowners should start here because it is free, faster, and often settles things without a hearing. If you're trying to decide between the two approaches, we break down the differences between informal and formal appeals so you can choose the right path.

Step 1: Confirm what you must beat

Look up your parcel's current enrolled value before you build a case. Use the county's ParcelQuest Lite property lookup.

Step 2: Build comps around January 1

Pick 3 to 5 comparable sales near your home that bracket the lien date. Contra Costa's Prop 8 form asks for sales no later than March 31, 2025 for 2025-26 reviews, which mirrors the formal rule that comps cannot be more than 90 days after the valuation date. Not sure what makes a good comparable or how to adjust for property differences? We cover the art of selecting and analyzing comparable sales in detail. If you're confused about which properties count or how adjustments work, dispelling common myths can save you hours of wasted effort.

Step 3: File the informal request by November 30

Send the Request for Value Review (Prop 8) to the Assessor by November 30, 2025. A county appraiser will compare your evidence and theirs. If January 1 market value is lower, they will enroll the lower number for the fiscal year beginning July 1.

Step 4: Watch the calendar

The Assessor delivers the assessment roll by July 1. If you disagree with the outcome or you have no answer as the formal deadline approaches, file a formal appeal on time to preserve your rights.

The Contra Costa "Formal" route (Assessment Appeal)

When the informal review does not resolve it, use the formal Assessment Appeals Board process.

Step 1: Check your window and your target

For regular roll values, the 2025 filing window is July 2 to December 1. For Supplemental or Escape assessments, you have 60 days from the notice date. Decide whether you are appealing a Decline-in-Value (Prop 8), a Base-Year value, New Construction, or another category on the BOE-305-AH application.

Step 2: File the application

Complete BOE-305-AH and mail it with a $40 check to the Assessment Appeals Board at 1025 Escobar St., 1st Floor, Martinez, CA 94553. One application per APN per roll year. If your property is in a trust, LLC, or held jointly, make sure you understand who can sign as a couple, trustee, or LLC to avoid standing issues. Signature problems are a common reason appeals get dismissed before anyone reviews your evidence.

Step 3: Prep like a pro

Your comps must be no later than 90 days after the lien date for Decline-in-Value cases. You can make a written Exchange of Information request under R&T § 1606 to see the Assessor's evidence before the hearing. Do this at least 10 days before the hearing. Want written findings of fact? The Board provides them for a fee and deposit.

Step 4: Hearing day

Hearings are typically scheduled on Thursdays at 9:00 a.m. You will be sworn in. You present first, then the Assessor. The Board can reduce, affirm, or increase the value based on the evidence. Stipulations are possible if you reach agreement beforehand.

DIY evidence checklist that actually works

What to include: Start with 3 to 5 comparable sales within about 0.5 to 1 mile, similar size, age, and condition, closing as close to January 1 as possible. Add a simple adjustment grid that explains differences. Include photos that prove condition, plus bids or reports for any deferred maintenance. Finish with a one-page summary stating your opinion of value on January 1 and why your property trails the comps. For insight into how county appraisers evaluate your evidence, see what assessors actually care about. When reviewing your property card, check whether land or improvements are driving the assessment increase—this can reveal the best angle for your appeal.

Frequently asked questions

Q: Do I need to reapply for Prop 8 each year?

No. Once a Prop 8 reduction is granted, the Assessor reviews it every lien date and notifies you by mail. You only appeal again if you disagree. Wondering about other common misconceptions? We tackle the top property tax appeal myths head-on.

Q: What if I disagree with the Assessor's informal Prop 8 result?

File a formal appeal within the July 2 to December 1 filing window for 2025.

Q: Where can I verify my parcel information and assessed value?

Use the county's ParcelQuest Lite property lookup.

Q: Can the Board raise my value at a hearing?

Yes. The Board can increase, decrease, or leave your value unchanged based on the evidence. Learn more about whether appealing can backfire and how to assess the actual risks involved.

How AppealArc helps

We pull same-neighborhood, same-vintage comps, build a lien-date-focused grid, and package it in a way assessors actually like to read. You handle the signature. We handle the nerdy parts.

Rules are local. Always verify the current instructions with Contra Costa County and county's official sites before filing.